It is proposed to continue measurements of magnetic circular dichroic (MCD) spectra of basic classes of organic chromophores in general and those of biological interest in particular, and to interpret these in terms of molecular orbital theories. In the first year and a half of the project, we have measured the MCD spectra of a variety of pi-electron systems and found to our pleasant surprise not only that semiempirical MO methods could be used for prediction of absolute signs of B terms in MCD spectra, but also that the origin of many of these signs can be deduced by inspection of Huckel MO's of the molecule or the parent hydrocarbon. We propose to continue both types of interpretative work: numerical calculations by more advanced methods, using both the sum-over-states and finite perturbation techniquas, as well as simple qualitative argumentation based on nodal properties of the MO's involved. Emphasis will gradually shift from the simple fundamental chromophores we have been dealing with so far to the biologically more important but also more complicated natural chromophores. Also, after about one additional year of work on pi-electron systems, we plan to initiate work on n and sigma electron chromophores, charge-transfer complexes, and the like.